Available Technology

Balancing and Control System for Operation of Multiple Cells and Packs in Large Energy Storage Arrays

Large scale energy storage systems, such as those used in electric vehicles or grid scale systems combine multiple electrochemical cells into a pack, or in the case of grid-scale systems, multiple packs into a large array of packs. However, battery packs often underperform due to cells or packs within the array having disparate states of health or performance capability. Consequently, the performance of the entire system is limited by the weakest unit. If these limits are unknown to a battery controller and the battery controller seeks to respond to a change in load, the nonlinearities imposed by the constraints can cause instability within the array and can lead to poor performance. In the case of electric vehicles, success is dependent upon the capacity and life of the battery. Distance limitations resulting from battery capacity constraints as well as the high cost associated with the replacement of electric vehicle batteries have made electric vehicles an expensive alternative to fossil fuel powered vehicles and inhibited widespread market acceptance. There needs to be a better method for battery control and optimization.
Patent Abstract: 
Scientists at NREL and other research organizations have developed an active balancing system for large arrays of multi-cell and multi-pack storage systems. This technology places a DC/DC converter at each individual cell, module or pack that can transfer power to and from that unit to a shared bus. By connecting the unit cell, module or pack via the shared bus, the shared bus can serve as the control reference and means to balance the power and energy delivery. The design allows for seamless communication amongst the units, possibly with different chemistries or states of health, to ensure that the entire array acts seamlessly as one system.
Benefits 
Extends lifetime of battery packs, including in a second-use environment -Reduces overall life cycle cost of battery packs -Balancing DC-DC converters can also supply an auxiliary load, eliminating need for a separate high voltage to 12V DC-DC converter in electric vehicle packs -Allows partial pack functionality with a failed cell or module
applications 
Internal Laboratory Ref #: 
ROI 14-33
Lab Representatives
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